A desirable property for an adhesive composition may be described as “cure-on-demand”. Adhesives that can be cured-on-demand characteristically have an extended (or indefinite) open time and can be rapidly cured at a desired time by the user.
Adhesive bonding two or more objects together has two objectives: a long open time (time before the adhesive cures) for applying the adhesive so that substrates are brought into reasonable alignment; and rapid curing of the adhesive once alignment has been completed. These interests are neatly summed up in the phrase “Cure on Demand” (COD), so often heard in the adhesive industry.
Cure on demand has been addressed in a variety of ways depending on the method used to effect curing. These methods include exposure to air or moisture, exposure to vaporous chemicals such as volatile amines, or exposure of the adhesive to heat or radiation or combinations thereof.
One type of cure-on-demand adhesive is ultraviolet (UV) light curable adhesives. These adhesives typically comprise a curable monomeric or oligomeric material (e.g., an acrylate or methacrylate) along with a UV sensitive initiator. Exposure of the uncured composition to UV light initiates cure of the adhesive on demand. Although UV curable adhesive are desirable, the adhesive to be cured must be positioned so that it can be conveniently exposed to the source of UV light in a direct “line of sight” relationship. Therefore, cure between opaque substrates cannot easily be achieved.